Using a corny keg as ball pressurizer is brilliant, cost effective solution guys! I'm an old homebrewer and have several laying around, so I'm totally psyched.

I just have one comment at this point concerning the keg type: Yes, the pressure relief valve is very nice on the ball lock keg style, but it is also VERY easy to release the pressure on a pinlock keg using a a small screwdriver. You can simply push down on either the air intake or outlet valves to release the air. If you can find pinlock kegs for significantly cheaper than balllock kegs, then I would go with the cheaper one--it's really easy and trivial to release the air in a pinlock keg and this really isn't a significant issue, imo.

I as well use a corny keg to extend the life of my balls. But I took a different approach, where I drilled out the emergency relief value and slipped a long stem tire valve through it, and it works like a charm with no air leaks. This way I can use my air compressor and pressure gauge without any hassle. It holds about 50 balls or so.

I got the Tennis Ball Charger 150 from Set US Tennis. I have been very happy with the result. The unit is equipped with a air valve on top so you can charge it with a compressor instead of the hand pump. It also comes with a special tool that allows you to tighten the cap so that it doesn't lose pressure over time. When I bought the device I had 144 Penn heavy duty balls about 2 weeks old which I use with a ball machine. I put the balls into the device and left them for 5 days and when I removed them they bounced just like new ones. There are only a couple of small negatives. The unit only holds about 140 balls, and you have to remove them manually rather than just dumping them out. It still only takes a couple of minutes. A little pricey at $300 but worth it in not having to fabricate something myself that may or may not work right. The benefit is saving money on balls and always having the correct bounce when I practice.

Can you give me the size and/or partnumber for the schrader valve you are used? Also, what size tubing are you using for the valve? (I have tubing that's 5/16" x 9/16" OD)

Thanks!
Ignac

You'll want 1/4" ID tubing. Mine is 1/4" ID x 3/8" OD. The thicker the wall on the tubing, the trickier it will be to fit the tubing over the air valve and the tank's disconnects. Heating the tubing with something like a hair dryer will make the tubing pliable enough where you can slip it over the barbed end of the disconnect and the tank side of the air valve.

Just go to your local auto parts store and ask for an air tank valve that has a 1/4" threaded end (got mine at O'Reilly). They cost around $2. Google "air tank valve" if you want to see pictures.

Just found this thread and thought I'd share what I've been working on... comments/suggestions welcome.

I just started playing again recreationally after a 20 year hiatus and find that the felt on the balls far outlasts the balls going "dead". My local county tennis center has ball machines for rent, and includes practice balls to be used in the machines. However, all of the balls are totally dead which makes practicing with them tedious and impractical.

My thoughts are to use a "paint pot" as mentioned here earlier in the thread. I bought one at HF for $80 ($100 less the 20% off coupon). I removed all the fittings (including the safety pressure release valve) and added a male inlet and a pressure gauge. The pot is steel, 2.5 gallons, and hold about 30 tennis balls.

So far, I've observed that the balls start to crush (you can hear them deforming inside the pot) at about 40psi. The pot from HF is relatively cheap and so the seal doesn't work very well. An easy solution for this is to just set your regulator for the desired pressure from your air compressor, and let it run and maintain the pressure in the pot as it leaks.

My plan is to chart out different pressures/durations to determine the most efficient pressure/duration for reviving a "dead" ball. For instance, I plan to take known dead balls (exposed to the atmosphere for at least 6 months), measure their rebound (using a rig I set up), then "pressurize" them at 15psi, 20psi, 30psi, etc. for 24 hours, 48 hours, 72 hours, etc. After each round in the pot, I'll retest their rebound to determine how much "bounce" is gained. It will probably take a few weeks to come up with the right blend of pressure/duration, but it seems like it'd be the most empirical way of doing this.

The commercial product that goes for several thousand dollars (and perhaps can only be leased) doesn't give much information other than 50psi and 4-5 days. Since there's no easy way to test the internal pressure of the balls, my thought is that the simplest solution is to measure the rebound when dropped from a specific height. My rig drops balls straight down from 100" as specified by the USTA. I plan to use my hi-speed camera to capture rebound height.

Just found this thread and thought I'd share what I've been working on... comments/suggestions welcome.

I just started playing again recreationally after a 20 year hiatus and find that the felt on the balls far outlasts the balls going "dead". My local county tennis center has ball machines for rent, and includes practice balls to be used in the machines. However, all of the balls are totally dead which makes practicing with them tedious and impractical.

My thoughts are to use a "paint pot" as mentioned here earlier in the thread. I bought one at HF for $80 ($100 less the 20% off coupon). I removed all the fittings (including the safety pressure release valve) and added a male inlet and a pressure gauge. The pot is steel, 2.5 gallons, and hold about 30 tennis balls.

So far, I've observed that the balls start to crush (you can hear them deforming inside the pot) at about 40psi. The pot from HF is relatively cheap and so the seal doesn't work very well. An easy solution for this is to just set your regulator for the desired pressure from your air compressor, and let it run and maintain the pressure in the pot as it leaks.

My plan is to chart out different pressures/durations to determine the most efficient pressure/duration for reviving a "dead" ball. For instance, I plan to take known dead balls (exposed to the atmosphere for at least 6 months), measure their rebound (using a rig I set up), then "pressurize" them at 15psi, 20psi, 30psi, etc. for 24 hours, 48 hours, 72 hours, etc. After each round in the pot, I'll retest their rebound to determine how much "bounce" is gained. It will probably take a few weeks to come up with the right blend of pressure/duration, but it seems like it'd be the most empirical way of doing this.

The commercial product that goes for several thousand dollars (and perhaps can only be leased) doesn't give much information other than 50psi and 4-5 days. Since there's no easy way to test the internal pressure of the balls, my thought is that the simplest solution is to measure the rebound when dropped from a specific height. My rig drops balls straight down from 100" as specified by the USTA. I plan to use my hi-speed camera to capture rebound height.

Sounds great. Just make sure to keep track of ball brands along the way. Two balls equally dead do bounce different heights if they are from different companies.
My experience is anything 25,30,40 etc doesn't work as well as 18-20 over a couple weeks. It will be interesting to see what results you get. Keep us posted, thanks!

I've been thinking about testing the "rebound" of the balls, and have decided that rather than spend the time and energy reviewing film, I'll likely just use the "thud" sound on the first and second bounces and compute the height by taking the time interval between bounces. I think this approach will be more practical, consistent, and faster.